The present invention relates to an environmental control apparatus for controlling a working environment in an exposure apparatus. More particularly, the present invention is concerned with an environmental control apparatus for an exposure apparatus for effecting exposure using exposure light having a wavelength range in which oxygen absorbs the exposure light.
In recent years, it has been desired to produce highly integrated semiconductor circuits. In order to produce such semiconductor circuits, exposure apparatuses have been widely used in which a circuit pattern formed on a reticle as a mask is transferred to a photosensitive substrate. Hence, there have been increasing demands for an exposure apparatus which is capable of forming an image of high resolution. As a technique for producing highly integrated semiconductor circuits, there has been known a technique which utilizes, as exposure light, light having a short wavelength, such as a g-line or i-line light emitted from a mercury lamp, KrF excimer laser light and ArF excimer laser light. Especially, as a technique for producing a DRAM (Dynamic Random Access Memory) of 1G, a technique which utilizes ArF excimer laser light having a wavelength as short as 193 nm has been proposed.
However, when ArF excimer laser light having a wavelength of 193 nm is used as exposure light for producing highly integrated semiconductor circuits, problems arise, such that the amount of exposure light which reaches the photosensitive substrate decreases and, therefore, becomes unstable during exposure. The causes of the above-mentioned problems are as follows:
(1) Light having a short wavelength, such as ArF excimer laser light of 193 nm, is absorbed by oxygen in an atmosphere. That is, ArF excimer laser light has a spectral range which includes a specific wavelength range in which oxygen absorbs the ArF excimer laser light. Therefore, in an exposure apparatus in which ArF excimer laser light is used as exposure light, when exposure is effected in a normal atmosphere comprising air having an oxygen content of about 20%, ArF excimer laser light is absorbed by oxygen during exposure. Therefore, the amount of exposure light which reaches the photosensitive substrate decreases during exposure.
(2) When oxygen absorbs ArF excimer laser light, ozone is produced. Since ozone also absorbs ArF excimer laser light, the amount of exposure light which reaches the photosensitive substrate progressively decreases and therefore becomes unstable during exposure, leading to difficulty in monitoring the amount of exposure light for which highly precise measurements are required.
Accordingly, it is presumed that the above-mentioned problems accompanying a technique which utilizes exposure light having a short wavelength can be obviated by removing oxygen in an area including a light path in an exposure apparatus in a manner such that the area is purged with an inert gas and sealed, or an inert gas is continuously supplied to the area for removing oxygen.
However, when the removal of oxygen in an area including a light path is conducted in such a manner as mentioned above, there are various disadvantages as follows:
(1) When an area including a light path is completely sealed, it is difficult to load and unload a mask and a photosensitive substrate in the light path.
(2) When an area including a light path is adapted to be sealable using a gate for loading and unloading a mask and a substrate, which is provided in a carrying means for the mask and substrate, it is difficult to periodically perform maintenance for a substrate stage.
(3) A sealing structure which has a large internal volume and is very complicated is required, due to a large degree of motion of a substrate stage.
(4) It is difficult to form a sealing structure having a sufficient pressure resistance against a difference in pressure between the interior and exterior thereof.
(5) When light is transmitted through a sealing structure having a large internal volume, the temperature distribution in the sealing structure becomes non-uniform, so that it is difficult to control the temperature of the sealing structure.
In view of the above circumstances, a primary object of the present invention is to provide an environmental control apparatus for use in an exposure apparatus for effecting exposure using exposure light having a wavelength range in which oxygen absorbs the exposure light, which has a simple construction and which suppresses a decrease in the amount of exposure light, so that the amount of exposure light can be stabilized during exposure.
According to the present invention, there is provided an environmental control apparatus for controlling a working environment in an exposure apparatus for effecting exposure using exposure light having a wavelength range in which oxygen absorbs the exposure light, which comprises an ozone removing filter for removing ozone in the air supplied to the exposure apparatus.
According to one preferred embodiment of the present invention, the environmental control apparatus further comprises an air conditioning system having an air circulation passage for supplying air having a controlled temperature to the exposure apparatus and the ozone removing filter is disposed in the air circulation passage of the air conditioning system.
According to another preferred embodiment of the present invention, the environmental control apparatus further comprises ozone concentration detection sensors which are disposed upstream and downstream of the ozone removing filter in a flowing direction of the air supplied to the exposure apparatus, and a device for detecting a degree of clogging of the ozone removing filter on the basis of outputs from the ozone concentration detection sensors.
When the environmental control apparatus of the present invention which comprises an ozone removing filter is used for an exposure apparatus for effecting exposure using exposure light having a wavelength range in which oxygen absorbs the exposure light, undesirable ozone which is produced from oxygen and absorbs the exposure light can be removed by the ozone removing filter. Therefore, the environmental control apparatus of the present invention is advantageous in that a decrease in the amount of exposure light can be suppressed and, therefore, the amount of exposure light can be stabilized during exposure. By use of the environmental control apparatus of the present invention, it has become unnecessary to form in the exposure apparatus a sealing structure for sealing an area including a light path. Therefore, the above-mentioned disadvantages accompanying a technique which utilizes a sealing structure (such as difficulties in loading and unloading a mask and a photosensitive substrate, performing maintenance, controlling a temperature of the sealing structure and the like) can be obviated. Although oxygen is relatively stable in a normal atmosphere and difficult to remove using a filter, ozone created by exposure light is relatively unstable in the same atmosphere and is highly reactive, so that it can be readily removed using a filter.
Since ozone has an adverse effect on a photoresist on the photosensitive substrate, the environmental control apparatus of the present invention is also advantageous in that an adverse effect on the photoresist due to ozone can be suppressed.